Self-healing materials are of interest due to their many potential applications, providing a unique promising platform for environmental and physiological applications. A self-healing polymer must possess the ability to form multiple bonding interactions in and around the damaged area, creating connections between the components that make up its structure. To date, this challenge has been treated with four different strategies: (a) encapsulation of reactive monomers that are released after a fracture, (b) the formation of new irreversibly covalent bonds in the damaged area, (c) supramolecular self-assembly, and (d) the formation of reversible covalent bonds.
Encapsulation of monomers has been used successfully for some applications, but the irreversible nature of the healing mechanism is a limitation, as the repair can occur only once in the same place. The same applies for irreversible covalent bonds that are induced in the damaged area. A particularly useful approach to generate self-healable polymers has been the introduction of reversible bonds or cross-links into the polymer network. Thus, chemical cross-links which are broken when the material fractures can be reconnected again, restoring the integrity of the material. However, most reversible covalent systems developed to date require the use of heat, light or other energy for the reaction to take place, which greatly limits its practical application.
WO2010128007A1 discloses a self-healing polymer comprising disulfide bonds, wherein self-healing is achieved by interchange reaction via the disulfide-bonds. Nevertheless, healing is only achieved after heating at temperatures higher to 60° C., and mechanical properties are fully restored only at the mentioned temperature after one hour.
WO2010087912A1 discloses a composite comprising the reaction product between a macromolecule comprising at least one thiol and a gold nanoparticle. The thiolated macromolecules cross-link with the gold nanoparticles to form a hydrogel which is useful for cell anchoring. Nevertheless the process takes place with a slow cross-linking speed (the hydrogel is obtained after a minimum of 24 hours from mixing the components) and reversible cross-linking can only effectively take place among freshly prepared hydrogel structural elements. Additionally, toxicity of Au nanoparticles is still a controversial issue in the scientific literature (Y-S. Chen, et al. “Assessment of the In Vivo Toxicity of Gold Nanoparticles”, Nanoscale Res. Lett., 2009, vol. 4, pp. 858-864).
While various self-healing materials have heretofore been disclosed in the literature, there continues being a need of a polymer system with self-healing properties providing superior benefits, especially in the biomedical field.